Geoscience Reference
In-Depth Information
C
HAPTER
8
CLUES FROM
THE FOSSIL RECORD
With respect to the apparently sudden extermination of whole
families or orders . . . we must remember what has already
been said on the probable wide intervals of time between our
consecutive formations; and in these intervals there may
have been much slow extermination.
Charles Darwin
W
HAT
E
XTINCTION?
Craters are physical features. Even one hidden under a kilometer of
rock can be discovered using geophysical techniques, then drilled,
and samples brought back to the surface and studied in the labora-
tory. As more and more craters have been discovered on earth using
such techniques, and as the evidence that Chicxulub is the K-T
impact crater has accumulated, more and more geologists have come
to agree that a giant impact ended the Cretaceous. Specialists have
calculated that the crash released the energy equivalent of 7 billion
bombs the size of the one dropped on Hiroshima, and produced the
loudest noise heard and the brightest light seen in the inner solar sys-
tem in the last 600 million years. Such an event, like the passage of
billions of years, is far beyond our experience and our ability to com-
prehend. Surely nothing could more clearly refute Hutton's maxim,
"The present is the key to the past." Confined as we are to the pres-
ent, it has taken geologists nearly 200 years to discover that large
meteorites have struck the earth and that terrestrial craters—many
of them—exist. That recognition leads to a new question: What are
the consequences of a giant impact for living creatures, such as those
that inhabited our planet 65 million years ago? On that point, far less
agreement exists. There is consensus, however, that the answer is to
be found in the fossil record.
